The NHS uses a standard set of BMI categories to screen adults for weight-related health risks. Whether your GP has mentioned your BMI, you've seen it on a health check form, or you're simply trying to understand what your number means — check it below, then read on for what each category means.
NHS adult categories are for people aged 18 and over. For ages 2 to 17, the NHS uses a separate calculator based on age and sex. Children and teens: NHS BMI calculator for children and teenagers. Ranges from NHS: Overweight and obesity in adults. BMI is a screening measure, not a diagnosis.
This guide covers the NHS ranges, what each one means, and the lower thresholds the NHS uses for some family backgrounds. It is not affiliated with the NHS; ranges are taken from nhs.uk, last checked 1 October 2026.
Looking for CDC ranges? See the CDC BMI categories for adults.
What Is BMI and Why Does the NHS Use It?
BMI stands for Body Mass Index. It is a number calculated from your height and weight using this formula:
BMI = weight (kg) ÷ height (m)²
BMI is useful as a first check because it needs nothing more than scales and a tape measure, takes seconds to work out, and uses the same formula everywhere, so results can be compared.
Important: BMI is not a diagnosis. It cannot tell the difference between muscle and fat, so the NHS also suggests checking your waist measurement against your height.
NHS BMI Categories 2026 — All Official Ranges
The NHS uses these BMI categories for adults aged 18 and over:
| BMI range | NHS category | What the NHS says |
|---|---|---|
| under 18.5 | Underweight | The NHS says people with a BMI under 18.5 are at risk of malnutrition |
| 18.5 to 24.9 | Healthy weight | The range between underweight and overweight |
| 25 to 29.9 | Overweight | Higher risk of conditions such as type 2 diabetes and high blood pressure |
| 30 or more | Obese | Higher risk of type 2 diabetes, heart disease, stroke and some cancers |
NHS BMI Healthy Weight Range — 18.5 to 24.9
For most adults, a healthy BMI is 18.5 to 24.9. Being in this range lowers the risk of the conditions linked to overweight and obesity, but it does not guarantee good health — diet quality, activity, smoking and family history all matter too.
These weights give a BMI in the healthy range. They are rounded inwards, so every weight shown is inside it.
Healthy weight ranges by height (metric)
| Height | Healthy weight (BMI 18.5 to 24.9) |
|---|---|
| 1.55 m | 44.5 kg – 60.0 kg |
| 1.60 m | 47.4 kg – 64.0 kg |
| 1.65 m | 50.4 kg – 68.0 kg |
| 1.70 m | 53.5 kg – 72.2 kg |
| 1.75 m | 56.7 kg – 76.5 kg |
| 1.80 m | 60.0 kg – 81.0 kg |
| 1.85 m | 63.4 kg – 85.5 kg |
Healthy weight ranges by height (stones and pounds)
| Height | Healthy weight (BMI 18.5 to 24.9) |
|---|---|
| 5′1″ | 7 st 0 lb – 9 st 6 lb |
| 5′3″ | 7 st 7 lb – 10 st 1 lb |
| 5′5″ | 8 st 0 lb – 10 st 10 lb |
| 5′7″ | 8 st 7 lb – 11 st 5 lb |
| 5′9″ | 9 st 0 lb – 12 st 1 lb |
| 5′11″ | 9 st 7 lb – 12 st 11 lb |
| 6′1″ | 10 st 1 lb – 13 st 7 lb |
Obesity Classes — Does the NHS Use Class I, II and III?
The NHS BMI calculator reports a single obese category for a BMI of 30 or more (27.5 or higher for the backgrounds listed below). It does not split obesity into classes on its public BMI pages.
You may still see obesity classes in letters or other guidance. The US CDC, for example, uses three:
| BMI range (CDC) | CDC category |
|---|---|
| 30 to less than 35 | Class 1 Obesity |
| 35 to less than 40 | Class 2 Obesity |
| 40 or greater | Class 3 Obesity (Severe Obesity) |
A higher BMI within the obese range usually means a higher health risk, which is why a GP may talk about where in the range you are, not just which category you are in.
Is NHS BMI the Same for Men and Women?
Yes — the NHS uses the same BMI categories for men and women.
The cut-offs at 18.5, 25 and 30 apply to all adults regardless of sex. Women tend to carry more body fat than men at the same BMI, which is one reason BMI is best used alongside other checks such as waist size.
NHS BMI Ethnicity Adjustments — Lower Thresholds for Some Groups
The NHS says that people from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background are at risk of health problems at a slightly lower BMI, so it uses lower thresholds for overweight and obesity. The calculator above applies them if you tick the family-background option.
| Category | Most adults | South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background |
|---|---|---|
| Underweight | under 18.5 | under 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 27.4 |
| Obese | 30 or more | 27.5 or higher |
In practice, a BMI of 24 is a healthy weight under the standard ranges but counts as overweight under the lower thresholds.
Waist Circumference — What the NHS Uses Alongside BMI
BMI cannot show where fat is stored. Fat around the tummy carries more health risk, so the NHS suggests a simple extra check: keep your waist size to less than half your height. If your BMI is under 35, you can use the NHS waist to height ratio calculator to check this.
Someone in the overweight range with a small waist may have a lower health risk than BMI alone suggests, and someone in the healthy range with a large waist may have a higher one.
NHS BMI vs CDC BMI — Are They the Same?
The main cut-offs at 18.5, 25 and 30 are the same. The differences are in who the categories cover and how the top of the scale is labelled:
| NHS (UK) | CDC (US) | |
|---|---|---|
| Adults from age | 18 | 20 |
| Underweight | under 18.5 | Less than 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to less than 25 |
| Overweight | 25 to 29.9 | 25 to less than 30 |
| Obese / obesity | One category: 30 or more | Three classes from 30 |
| Lower thresholds for some backgrounds | Yes | No |
What to Do If Your BMI Is Outside the Healthy Range
If your BMI is in the overweight or obese range:
- See a GP if you want help to lose weight, your waist is more than half your height, or you have a condition such as diabetes or high blood pressure
- The NHS says losing just 5 to 10% of your body weight can improve your health
- Aim to lose weight steadily — the NHS suggests 0.5 to 1 kg (1 to 2 lb) a week
If your BMI is in the underweight range:
- Speak to your GP — being underweight carries its own health risks, including malnutrition
- Your GP may refer you to a dietitian or look for an underlying cause
If your BMI is in the healthy range:
- Maintain it through a balanced diet and regular physical activity
- Check your waist against your height for a fuller picture
Summary — NHS BMI Categories 2026 Quick Reference
| NHS category | Most adults | Lower thresholds |
|---|---|---|
| Underweight | under 18.5 | under 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 27.4 |
| Obese | 30 or more | 27.5 or higher |
Want to switch between NHS and CDC ranges? Use the full BMI calculator.
Frequently Asked Questions
What are the NHS BMI categories in 2026?
For adults aged 18 and over, the NHS uses four categories: underweight (under 18.5), healthy weight (18.5 to 24.9), overweight (25 to 29.9), obese (30 or more).
Is the NHS BMI scale the same for men and women?
Yes. The NHS adult BMI categories are the same for men and women.
What is the NHS healthy BMI range for adults?
18.5 to 24.9 for most adults. For people from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, the NHS treats 23 to 27.4 as overweight, so the healthy range is 18.5 to 22.9.
What BMI does the NHS classify as obese?
A BMI of 30 or more for most adults, or 27.5 or higher for people from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. The NHS BMI calculator reports one "obese" category; it does not split it into classes.
What BMI is underweight according to the NHS?
A BMI under 18.5. The NHS says people with a BMI under 18.5 are at risk of being malnourished, so if you are underweight and not trying to be, speak to a GP.
Can I use the adult BMI categories for children?
No. The NHS adult BMI calculator is for people aged 18 and over. For ages 2 to 17, use the NHS BMI calculator for children and teenagers, which takes age and sex into account.
How does the NHS calculate BMI?
BMI = weight in kilograms ÷ (height in metres × height in metres). The NHS example: 70 kg and 1.70 m gives 70 ÷ 2.89 = 24.2, which is a healthy weight.
Sources: NHS: Overweight and obesity in adults; NHS: Calculate your BMI for adults; NHS: Malnutrition. Last checked 1 October 2026.
Medically reviewed: no. For information only, not medical advice. Talk to your GP about your weight and health.
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